In wireless devices, reception characteristics are measured at any time, self-correction is performed based on the measured reception characteristics, and thus high performance and high stability are achieved with low power consumption. To do this, a test signal generation circuit that generates a test signal is provided in a receiver circuit of a wireless device, and the generated test signal is supplied to the receiver circuit. A receiver circuit having such a test signal generation circuit is referred to as a receiving built-in-self-test (BIST) circuit.
In a receiver circuit, a local signal having a frequency close to that of an incoming signal is supplied to a mixer together with the incoming signal, a baseband process is performed in the mixer, and a transmission signal component is thereby extracted. In order to inspect reception characteristics, a signal simulating an incoming signal has to be generated separately, and be input from the immediate vicinity of an antenna.
Thus, a test signal generation circuit having a configuration similar to that of a local signal generation circuit that generates a local signal is installed, and a test signal is input from the immediate vicinity of the antenna by using a coupler or the like. The test signal is received by the receiver circuit, and is subjected to a baseband process. This enables measurement of reception gain, a phase change, and so forth.
The local signal generation circuit and the test signal generation circuit are each typically constituted by a phase locked loop (PLL) circuit, and control output frequencies by changing their respective division ratios. For example, a frequency of a signal generated by a voltage-controlled oscillator (VCO) is divided, a phase of this frequency-divided signal is compared with a phase of a reference signal, and a comparison result is fed back. Thus, feedback is applied so that a frequency of the frequency-divided signal becomes equal to a frequency of the reference signal. When a feedback loop is stabilized, an output frequency of the VCO is stabilized.
A frequency of a test signal has to be different from a frequency of a local signal. Hence, a signal source for test signal generation is installed separately from a local signal source, and frequency dividers installed in these respective signal sources have to be controlled so that their respective division ratios differ from each other. For this reason, the test signal generation circuit results in increases in power consumption and circuit area. In particular, in a frequency divider circuit provided in the test signal generation circuit, the conversion from an output frequency to a reference frequency has to be carried out, high-speed operation is demanded, and a significantly large division ratio is also demanded. Thus, the frequency divider circuit provided in the test signal generation circuit is large in size, and also consumes a large amount of power.
The following is a reference document.
[Document 1] Japanese Laid-open Patent Publication No. 2011-130174.